640 YELLOW FEVER 



surfaces, causing, in the case of the stomach, the " black vomit " 

 one of the clinical signs of the disease in its worst form. 

 Anuria, coma, and cardiac collapse usher in a fatal issue. The 

 mortality varies in different epidemics from about 35 to 99 

 per cent, of those attacked. Both white and black races are 

 susceptible, but those who have resided long in a country are 

 less susceptible than new r immigrants. An attack of the disease 

 usually confers complete immunity against subsequent infection. 



Post-mortem the stomach is found in a state of acute gastritis, 

 and contains much altered blood derived from haemorrhages 

 which have occurred in the mucous and submucous coats. The 

 intestine may be normal, but is often congested and may be 

 ulcerated ; the mesenteric glands are enlarged. The liver is in 

 a state of fatty degeneration of greater or less degree, but often 

 resembling the condition found in phosphorus poisoning. The 

 kidneys are in a state of intense glomerulo-nephritis, with fatty 

 degeneration of the epithelium. There is congestion of the 

 meninges, especially in the lumbar region, and haemorrhages 

 may occur. The other organs do not show much change, 

 though small haemorrhages under the skin and into all the 

 tissues of the body are not infrequent. In the blood a feature 

 is the excess of urea present, amounting, it may be, to nearly 

 4 per cent. 



Etiology of Yellow Fever. Although a large amount of 

 bacteriological work has been done on yellow fever, this has 

 merely a historical interest, as it is now known that the 

 causal agent is not one of the ordinary bacteria, but belongs to 

 the group of ultra-microscopic organisms. 1 A mosquito acts as 

 the intermediate host, and the facts detailed below point to the 

 organism passing through some cycle of development in the 

 body of the insect. The analogy of malaria makes it extremely 

 probable that the organism is a protozoon, but this has not yet 

 been completely proved. As bacteriological work led up to the 

 establishment of our knowledge regarding the nature of the 

 disease, some reference must be made to it. 



A very full research into the bacteriology of yellow fever was- 

 that of Sternberg, and one of the organisms isolated, which he 

 called the bacillus x, appeared possibly to have some relationship 

 to the disease. Sanarelli in 1897 isolated an organism Avhich he 

 called bacillus icteroides, and which he considered to be the 

 cause of yellow fever ; it was probably identical with the bacillus 



1 In several diseases the existence of such causal factors is probable. 

 Examples in animals are foot and mouth disease, South African horse sickness, 

 and the contagious pleuro-pueumonia of cattle. 



